1. Field of the Invention
The present invention relates to activated carbon adsorption systems for removal of certain compounds or contaminants from water and other fluid flow streams. More particularly, the present invention relates to a method and apparatus for continuous pulsed regeneration and sterilization of activated carbon used in the bed of an adsorption column.
2. Description Of The Prior Art
Activated carbon is a substance derived from coal, wood and other carbonaceous materials having great porosity, permeability and pore surface area. For reason of such great pore area, activated carbon is an excellent adsorber from water of dissolved organic and some inorganic compounds. When such carbon affinitive compounds are considered contaminants to a water stream, the contaminations may be removed by merely flow contacting the water stream with a bed or slurry of activated carbon.
Beds of activated carbon are also effective to remove, via filtration, bacteria from potable and process water streams. As a consequence, however, bacteria are trapped by the carbon bed in a climate favorable to growth and proliferation. As the bacteria colonies grow in the carbon bed, the stream flow is restricted and the effluent water stream from the bed is contaminated.
Disinfecting compounds such as chlorine, chlorine dioxide and chloramines as would normally be used to control such bacteria growth are ineffective in an activated carbon bed due to neutralization of the disinfectant by carbon adsorption.
Accordingly, bacteria growth control within an an activated carbon bed must be accomplished by such means as frequent backwashing followed by caustic washing and steam sterilization. But backwashing may only be used in unconfined beds i.e. contact volumes of carbon contained within vessels of substantially greater volume. Packed filter beds in which the carbon bed occupies substantially all of the vessel volume are not susceptible to backwashing. In these cases, steam/or caustic may be used.
Independent of confined carbon bed plugging and sterilization problems due to in situ bacteria growth, each activated carbon particle or granule may be compared to an independent vessel. Notwithstanding the affinity of activated carbon for certain compounds, the capacity for such is finite. Eventually, the particle vessel fills: a condition characterized as saturated or spent. When this occurs, the particle is of no further value for the adsorbent purpose and must be either replaced or regenerated.
Activated carbon regeneration is a process whereby the adsorbed compounds are removed from combination with the carbon particles i.e. the particle vessel is emptied of its contents. Thermal regeneration involves heating the carbon with combustion products to temperatures of 1500.degree. F.-1800.degree. F. in a controlled atmosphere for thermal destruction of the adsorbed compounds. Steam regeneration, in addition to sterilization, desorbs the adsorbed contaminants from the carbon heating the bed to the boiling point of the contaminants. Chemical regeneration comprises contacting the spent carbon with a highly reactive aqueous acid or caustic solution to react the adsorbed compound into solution with a pumpable fluid.
Due to the extreme thermal or chemically reactive environment of regeneration, the regenerative process is not normally performed in the adsorbent bed vessel. Standard flow stream adsorption contacting vessels are fabricated from mild steel and given an inexpensive abrasion and chemical resistant interior lining or coating. If the vessel is to be used for steaming or regeneration of the carbon charge, the entire vessel must normally be fabricated of a thermally and chemically resistant material such as stainless steel. Moreover, if continuity of the treated water flow stream is essential, the number of adsorption/regeneration vessels must be multiplied so that flow stream treatment may continue through a useful carbon bed during the time period a spent carbon bed is regenerated.
Treatment system multiplication of adsorption vessels is often necessary due to other considerations such as removal of a vessel from the treatment line for backwash removal from the carbon bed of non-adsorbed filterant and for steam sterilization heating periods. When the expense of multiple adsorption vessels, each with an over-sized backwash volume capacity, is compounded by the cost of constructing all such vessels from stainless steel, in situ carbon regeneration capacity is difficult to economically justify.
It is therefor, an object of the present invention to teach the construction and operation of a substantially continuous treatment activated carbon adsorption system which minimally requires only one, mild steel adsorption vessel and a pair of considerably smaller stainless steel blow cases for on-site carbon washing, sterilization and regeneration, as well as carbon transfer.
Another object of the invention is to minimize the size and value of support equipment required for a steam sterilization and regeneration plant sufficient to sustain an activated carbon treatment bed.
Another object of the invention permits substantially uninterrupted adsorber operaton with a single absorber vessel.